Telecommunication service providers have typically provided their customers with test access connection (TAC) capability for circuit-switching systems in order to monitor a given point-to-point call or connection. A monitor TAC basically converts a point-to-point connection into a point-to-multipoint connection, wherein one of the multipoints is the original connection endpoint and the other, new, endpoint or leaf terminates at a TAC port which is connected to test equipment. The switching technologies typically used in circuit-switched networks, e.g., step-by-step, panel & crossbar switching cores, conveniently enable a point-to-point connection to be converted into a point-to-multipoint connection on-the-fly, i.e., while the call is in progress, without disrupting the original call. This is because the added connection or new leaf is typically merely a parallel electrical connection in the switching core.
Customers of connection orientated packet-switching systems have also desired to be provided with monitor TAC capability. However, conventional connection-orientated packet-switching technologies typically do not enable a packet stream to be monitored without causing service disruption. This is because, simplistically speaking, connection-orientated packet switches typically employ some sort of look up routing table to provide the necessary internal addressing to route packets of a point-to-point connection through the switch, i.e. from an ingress card servicing an input port to an egress card servicing an output port. The output of the lookup table is typically added as overhead information to the packet which is examined by various components of the switch in order to implement the internal routing function. In order to convert a point-to-point connection into a point-to-multipoint connection, the look up table typically has to be modified to provide different overhead information which indicates to the internal switch components that the packet has to be copied, multi-cast or otherwise addressed to multiple endpoints on one or more output ports. This generally requires the packet switch to tear down the point-to-point call and re-setup the call as a point-to-multipoint connection, causing significant service disruption.